Process for producing tetrafluoroethylene polymer compositions



Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCINGTETRAFLUORO- ETHYLENE POLYMER COMPOSITIONS John Frank Lontz, Nutley, andLester Eugene Robb, Rutherford, N. J., assignors to E. I. du Pont deNemours & Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Application June 30, 1950,

Serial No. 171,536

This invention relates to new compositions comprising coagulatedtetrafluoroethylene polymer and particular hydrocarbon lubricants.

It has been. known previously that finely dividedpolytetrafiuoroethylene can be dispersed in various organic media, aswell as in an aqueous suspension. It has also been known thatpolytetrafluoroethylene can be fabricated into shaped articles bysubjecting the finely divided polymer to pressure, and thereafterheating the resulting article at a temperature above 327 C. untils-intered, and cooling the sintered shaped article.

Although highly valuable and useable, these preing same. Other objectswill be apparent from the description of the invention given below.

The above objects are accomplished according to this invention by theprovision of non-aqueous pressure-coalescing compositions comprisingcolloidal particles of tetrafluoroethylene polymer, which in particularembodiments have been coagulated from an aqueous colloidal suspension,of

the polymer, intimately admixed with at least.

one essentially saturated aliphatic and/or cycloaliphatic hydrocarbon,normally liquid at C.,

and having a boiling point of 220-400 C. atatmospheric pressure, saidhydrocarbon being present in an amount equal to from 15% to of thecombined weight of said polymer and hydro! carbon. It is preferred toemploy a hydrocarbon or mixture of hydrocarbons having a boiling pointMoreover, these previously Another ob- I je'ct is to provide new anduseful lubricated polytetrafluoroethylene compositions in the form of adry molding powder and methods for prepar-' 5 Claims. (Cl. 260-335)rafiuoroethylene homopolymer), it is to be understood that the inventionalso applies to other tetrafluoroethylene polymers. Thus,tetrafiuoroethylene copolymers comprising the polymerization product ofa mixture of tetrafluoroethylene and-another unsaturated organiccompound (e. g., ethylene and chlorotrifluoroethylene) containing aterminal ethylenic double bond, said organic compound beingcopolymerizable with tetrafluoroethyl'ene and being present in saidmixture in an amount of up to 15% of the combined. weight oftetrafiuoroethylene and said organic compound, may be employed in placeof polytetrafiuoroethylene, provided the presence of the other compoundsdo not destroy the essential and characteristic qualities of thecolloidal particles.

Also there may be employed tetrailuoroethylene polymers in which the endgroups of the polymer chain are supplied by non-polymerizable compounds(e. g., methanol and ethanol) which are present during thepolymerization reaction. The

tetrafiuoroethylene polymers employed in the: practice of this inventionembrace the above three types of polymers, it being understood that allthe tetrafluoroethylene polymers of this invention possess a high degreeof polymerization and a sintering temperature of at least 300 0.

Above the sintering temperature such polymers form a gel butthey do notactually melt to a liq- ;uid. This is in contrast to the knownrelatively low molecular weight polymers derived fromtetrafiuoroethylene and certain tetrafluoroethylene polymer waxes, bothof which have sharp melting points.

The thoroughly dry non-aqueous lubricated polymer compositions of thisinvention, which may be prepared by various methods describedhereinafter, are pulverulent solids. sitions as prepared are suitablefor directly extruding, calender-rolling, coating, molding, or otherwisefabricating'into finished articles without further special treatment.

The following examples illustrate specific embodiments of thisinvention. All parts are by weight unless otherwise specified, and allaqueous colloidal polymer suspensions were prepared as described in U.S. Serial No. 107,137, filed July 2'7, 1949, by K. L. Berry. The latterapplication discloses the. polymerization of tetrafiuoroethylone at 0 toC. in an aqueous medium in the presence of a water-solublepolymerization catalyst such as disuccinic acid peroxide, i. e.,

'(HOOCCI-IzCI-IzCOO) 2,

The compoand. an alkali metal or ammonium salt of an acid of theformula,

H(CF2CF2) 3 to COOH These acids are obtainable by oxidizing, with apermanganate oxidizing agent, a polyfiuoroalkanol of the formula,

The latter compounds are in turn formed by polymerization oftetrafiuoro-ethylene in the presence of methanol and an organic peroxidecatalyst at a temperature between 75 C. and 350 0., as disclosed in U.S. Serial No. 65,063, filed by R. M. Joyce on December 13, 1948, nowPatent Number 2,559,628.

Example 1.-One hundred twenty-five parts of a 60% solids aqueouscolloidal suspension of polytetrafluoroethylene (75 parts polymer and 50parts water) is extended with 167 parts distilled water. To this isadded parts of a commercial grade of white mineral oil '(i. e. liquidpetrolatum, known as Primol) consisting of a naturally occurring mixtureof parafi'inic and naphthenic hydrocarbons substantially free ofunsaturates (average molecular weight 413.5; boiling range 330-390 C.;viscosity 115.6 cps. at 26 C.). The resulting mixture of aqueous polymersuspension and oil is whipped to an emulsion in a Waring Blendor while amixture of 83 parts water and 66 parts acetone is added to coagulate thedispersed polymer. After approximately 3 minutes of agitation followingthe completed addition of the aqueous acetone, the lubricated coagulatedpolymer is filtered under strong suction and dried at 110 C. to expelany occluded water.

The resulting dried mixture is a soft, white, nearly grainy productwhich is readily extruded, calender-rolled, or molded into all sorts ofshapes. The lubricant remaining after these fabricating operations maybe removed either by extracting in such solvents as hexane, naphtha,toluene, etc., or volatilizing in a heated chamber. The lubricant-freearticle is then fused to a hard, tough material by heating at atemperature above 327 C., the transition point of the polymer.

The following illustrates the utility of the above dry, lubricatedmolding powder composition. The composition is placed in an extrusionchamber fitted with an hydraulically-operated piston to force thelubricated polymer sidewise through a circular orifice tapered to a.0.040-inch opening, thereby forming a continuous length of a circularbeading or filament. The extrusion is accomplished at room temperaturewith a pressure of approximately 2,000 lbs. on a 1.25 inch diameter ram.In this form, the lubricated polymer mixture is particularly suited forrolling into a tape or ribbon-like material by passing between a pair ofcalendering or smooth-surfaced rolls. From the 0.040-inch beading a tape0.34-inch wide and 0.006-inch thick is formed. This tape is next freedof the contained lubricant by immersing in toluene which serves as anextracting solvent. The tape is then sintered by passing through a pipe,l-inch in the inside diameter, electrically-heated to an innertemperature of 350-380 C. The resulting tape has a neartransparent,bluish appearance. On testing, it shows an average tensile strength of3220 lbs/sq. in. and an average elongation of 200 per cent as determinedby the A. S. T. M. test method designated as D-412-41. The tape made bythis method is useful as a dielectric insulation for such electricalcomponents as cables, coils, armatures, etc.

Example 2.A lubricated polymer composition in the form of a dry powderis prepared by the same procedure as described in Example 1 but usinginstead 81.8 parts of polytetrafluoroethylene and 182 parts of whitemineral oil.

The dry powder is placed in an extrusion chamber fitted with anhydraulically-operated piston to force the lubricated polymer through aslit die 1.50 inches wide with a 0.010 inch opening, forming acontinuous length of a fiat ribbon or tape. In this form, the lubricatedpolymer mixture is particularly suited for rolling into even thinnerribbon or tape to a thickness down to 0.0005 inch. This tape is nextfreed of the contained lubricant by extracting in toluene. The extractedtape is then sintered by passing through a heated chamber at atemperature of 350-380 C. The resulting tape has a neartransparent,slightly opalescent appearance with the characteristic toughnessequivalent to polytetrafluoroethylene fabricated by other methods suchas molding.

Example 3.An aqueous colloidal suspension of polytetrafluoroethylene iscoagulated by highspeed stirring and the coagulated polymer is filteredby suction and dried at 110 C. To 119 parts of methanol are added partsof the dried coagulated polymer and 2.38 parts of a polyethylene glycolether of an alkylated phenol (an nonionic dispersing agent knowncommercially as Triton N-) in a Waring Blendor, and the resulting slurryis agitated at moderate speeds. To the mixture is added 25 parts of acommercial grade of cetane (distillation range 252 C.-274 C.; viscosity3.5 cps. at 25 C.) with agitation, which is continued for 15 secondsafter the addition is completed. The lubricated polymer is filteredunder suction giving a filter cake that resembles a fine powder. Thispowder is dried at C. in an air oven for 20 minutes to remove anyretained methanol.

The lubricated polymer is suitable for extrusion into beading, tape,tubing, or as coating on wire by extrusion. The cetane is removed fromthe extruded form by vaporization in an air oven and the polymer isfused to complete particle coalescence at temperatures above itstransition point, 327 C.

Example 4.--Eighty parts of the same coagulated dried unlubricatedpolytetrafiuoroethylene as that used in Example 3 is placed in thebottom of a closed rotatable double-cone blender having a tubular shaftthrough which liquid may be introduced from an exterior reservoir. Inthis blender the shaft is provided with a pair of misting nozzlesthrough which 20 parts of cetane, the same as that used in Example 3, isslowly forced from the reservoir by means of air or nitrogen pressure. Aby-pass from the pressure source is introduced to the orifice within thecetane line so that the gas passing through the orifice atomizes anddilutes the cetane to produce a fine mist at the nozzle exits. Theinjection is started by applying an air or nitrogen pressure of 50lbs/sq. in. to the reservoir and the by-pass orifice. The injection rateis controlled to 0.0125 part of cetane per minute per part of polymer.The blender is meanwhile rotated at a speed of 15 R. P. M. during 20minutes of injection and 30 minutes of subsequent blending. After thecompletion of this typical cycle, the lubricated polymer in the form ofa dry, free-flowing powder is then withdrawn and is ready for rolling,extrusion, and other forming operations for making film, sheeting,filament, or coating on wires.

The tetrafiuoroethylene polymer for use in this invention may beobtained by coagulating an aqueous colloidal suspension of the polymer.It has been found that other finely divided forms ofpolytetrafiuoroethylene, such as the granular form obtained by directpolymerization in accordance with U. S. Patents 2,230,654; 2,393,967;and 2,394,243, the micro-pulverized form, or any other form which hasbeen mechanically, sub-divided from the massive polymer cannot readilybe extruded or molded under pressure to yield satisfactory articles. Forexample, when the granular form ofpolytetraiiuoroethylene.preparedaccording the above patents and thendisintegrated into small particles, is mixed with cetane (75% polymer,25% octane), one of the preferred hydrocarbons for use in thisinvention, and extruded into tape through a 0.010 inch slit die atapproximately 26 C., the mixture of polymer and octane extrudes' as anon-cohesive powder. The octane actually exudes from the mixture uponapplication of sli ht pressure, resulting in a discontinuous tape ofnon-uniform caliper. The granular poiymer/cetane mixture is quitedifferent from the corresponding coagulated polymer/cetane mixture inthat the former shows no pressure-coalescing property when pressed on aflat surface, whereas the pressure-coalescing property is characteristicof the latter compositions.

i The process of preparing the aqueous suspen sion oftetrafluoroethylene polymer is not the subject or" this invention.However, suitable aqueous suspensions of polytetrafluoroethylene may beobtained by the methods described in U. S. SerialNo. 713,385, filedNovember 30, 1946, by M. M. Renfrew, now Patent Number 2,534,058, U. S.Serial No. 107,137, filed July 27, 1949, by K. L. Berry, and U. S.Patent 2,478,229. Aqueous suspensions of tetrafluoroethylene copolymersmay be obtained by the methods described in U. 8. Serial No. 107,137,filed July 2'7, 1949, by

L. Berry. Aqueous suspensions of tetrafluoroethylene polymers in whichthe end groups of the polymer chain are supplied by non-polymerizablecompounds may be obtained by the same method as that described for thepreparation of the polytetrafiuoroethylene suspension as typified byBatch D of Example X in U. S. Serial No. 107,137, filed July 2"], 1949,by K. L. Berry, except that, for example, 0.075 part of methanol as thenonpolymerizable compound is added with the other reactants to thepressure vessel prior to polymerization. The particle size of thepolymer evidently is rather highly critical, i. e., it should becolloidal'beiore coagulation, and the smaller the particles the moreeasily the lubricated composi--' tion may be fabricated into articles.The particle size of the polymer in the suspensions described in theabove-mentioned applications and patent in general ranges from 0.05 to 5microns, which is the diameter of the average particle determined by anelectron microscope measurement on a dried film obtained by depositing ahighly diluted aqueous suspension of the polymer on a surface. Thesecolloidal suspensions have been found quite suitable for coagulation inpreparing the compositions of this invention. The colloidal particles ofpolytetrafiuoroethylene retain their particulate form during coagulationalthough agglomeration may occur to some extent, whereby individualparticle's attach themselves to other particles without necessarilylosing their identity,

but this does not aiiect their ability to be fabricated when combinedwith the hydrocarbons of this invention. The coagulated mass is thus acharacteristic physical form of the polytetrafluoroethylene. Moreover,polytetraf'luoroethylone is Virtually insoluble in practically all knownsolvents, and therefore the particlesdo not coalesce when merelysuspended in organic media. To coalesce the particles in the compositionof this invention it is necessary to subject them to the action of heatand/or pressure. The colloidal particles possess marked adsorptiveproperties, and can be employed, for example, as adsorbents forhydrocarbons in much the same manner as charcoal or other highlyadsorptive solid materials. In this respect the colloidal form ofpolytetrafluoroethylene differs from other finely divided forms of thepolymer.

There are several reasons why the properties of a particular group ofhydrocarbons is critical in this invention. As set forth above, either asingle hydrocarbon or a mixture of two or more synthetic ornaturally-occurring hydrocarbons may be used, but they should benormally liquid at 25 C. (i. e., at atmospheric pressure) and shouldhave a boiling point in the range of 220 C. to 400 C. Although severalmethods of preparing the lubricated compositions of this invention havebeen disclosed herein, by far the best results are obtained by mistingthe hydrocarbon onto the dried polymer particles. This method yields themost homogeneous compositions with respect to uniform incorporation ofthe lubricant throughout the mass of polymer particles. Small degrees ofnon-homogeneity in the compositions show up in large variations inpressure during extrusion of the compositions if the hydrocarbonlubricant has not been uniformly incorporated so that each polymerparticle is surrounded by a liquid film of the hydrocarbon.Consequently, the hydrocarbon should be liquid at room temperature (i.e. 25 C.) to readily permit spraying or atomizing the hydrocarbon underpressure in the form of a fine mist or fog, which is generally propelledin a stream of inert gas such as carbon dioxide or nitrogen to permitadequate control of the misting rate. The hydrocarbon could be a solidat 25 C. and be dissolved in a solvent and the solution sprayed onto thepolymer particles; however, the solvent then would have to be removedwhich is an additional step requiring added time and expense.Furthermore, it is much more difiicult to control spraying of a solutionthan of a liquid of relatively narrow boiling range.

The preferred boiling range for the hydrocarbon is 250 C. to 300 C. Thelower limit of the boiling range is set by the volatility of thehydrocarbon during extrusion under pressure.

.By this is meant that a hydrocarbon boiling much below 250 C. atatmospheric pressure volatilizes too rapidly during room temperatureextrusion of the lubricated polymer at commercial rates (and even morerapidly at elevated extrusion temperatures) to permit accurate control'of the caliper of the extruded articles. In other words, starting with alubricated polymer containing 18%of lubricant of a boiling point say C.,it has been found that upon analysis the'extruded article'beforeintentional removal of the lubricant and before sintering may containonly 10% of lubricant, the remaining lubricant having been lost duringthe extrusion operation. Furthermore, these particular extruded articlesare not of reproducible caliper; that is,

7 tapes, filaments and coatings over wire cannot be held to closetolerances without constant manual control and supervision throughoutthe extrusion operation. Even though constant vigilance attends theextrusion, the pressure variations due to loss of lubricant may be toogreat and the changes too rapid to hold the caliper constant even withrepeated manual adjustments. The upper limit of the boiling range of thehydrocarbon is set chiefly by a balance between two factors; i. e., thetime required for removing all of the hydrocarbon prior to sintering theextruded articles and the amount of charring which occurs in exposingthe extruded article containing the hydrocarbon to elevatedtemperatures. By way of explanation, it is deired to use a hydrocarbonwith as low a volatility as possible to permit ready removal byvolatilization within a short time, and further it is preferred toremove substantially all of the hydrocarbon prior to the time when theextruded article reaches the sintering temperature (i. e., 327 C. forpolytetrafluoroethylene). Prolonged heating of the extruded articlescontaining hydrocarbons, especially those having boiling points above325 C., results in a certain amount of charring, and in general, thelonger the heating cycle the greater the charring. This charringincreases the power factor and dielectric constant of the sinteredshaped article which 7 is quite undesirable for some of the moreimportant electrical applications for polytetrafluoroethylene. Inaddition, as the boiling point of the hydrocarbon rises above 325 C.,the melting point also begins to rise so that very soon the hydrocarbonsare no longer sprayable at room temperature, which is a disadvantage.From the above discussion, it will be seen that a relatively narrowrange of hydrocarbons is particularly Valuable for Carrying out theobjects of 4:; particles are being tumbled in a rotating blender.

this invention in providing a combination of (1) a rapid effectivemethod of incorporating the hydrocarbon into the polymer particles, (2)a method of extruding the lubricated polymer with a minimum of effortand control to obtain shaped articles of reproducible caliper, and (3) amethod drocarbons, but these do not interfere withthe practice of thisinvention, and for this reason the hydrocarbons are termed essentiallysaturated.

The proportion of hydrocarbon in the compositions is as criticallyimportant as the properties of the hydrocarbon. Compositions containingmuch less than 15% of. the hydrocarbons of this invention reduce therate of extrusion to such an extent that abnormally high pressuresdevelop and cause fibering of the polymer during. extrusion. If morethan 30% hydrocarbon isused, the shrinkage of the sintered articlebecomes too great and in some cases cracks and fissures may develop dueto abnormally high shrinkages.

The larger proportions of hydro-- iii carbon allow anincreased rate ofextrusion at decreased pressures, but as pointed out, there is a limitin that too much hydrocarbon in the lubricated polymer will yield acomposition which has a soupy consistency and is difficult to handle inthe extruder, mold, or other fabricating apparatus. Also, too great aproportion of hydrocarbon means that the fiow of the composition and thedeveloped pressure cannot be controlled to give accurate tolerances inthe fabricated articles, as well as preventing uneconomicaldisadvantages in removal of the hydrocarbon lubri-' cant. Allpercentages of hydrocarbons throughout the specification are based uponthe combined weight of dry tetrafiuoroethylene polymer and hydrocarbonin the composition.

The compositions of this invention may be prepared by a variety ofmethods. One such method comprises intimately mixing the hydrocarbonwith an aqueous suspension of colloidal polyte'trafiuoroethylene underhigh speeds of agitation with or without a dispersing agent, followed bycoagulation accomplished by the addition of either an electrolyte or awater-miscible organic liquid such as acetone or alcohol. In this methodit is preferred to use one of the many suitable dispersing agentsdisclosed in U. S. Patent 2,478,229. An equally satisfactory method forobtaining the compositions involves coagulating an aqueous suspension ofcolloidal polytetrafiuoroethylene, drying the coagulated polymer,suspending the coagulated polymer in an organic liquid vehicle which maybe soluble in the hydrocarbon (e. g., methanol or tertiary butanol), andthen adding the hydrocarbon with continuous stirring, followed byfiltering or evaporation of the'suspending vehicle. A third methodcomprises spraying a mist of the hydrocarbon onto the dry coagulatedpolymer particles While the fourth method employs high speed agitationof the dried coagulated polymer in the presence of the hydrocarbon. Theonly requirement for preparing satisfactory compositions is tothoroughly and intimately disperse the hydrocarbon throughout theparticles of the coagulated polymer. As pointed out above, it ispreferred to use the spraying method for preparing the compositions ofthis invention because this method yields far superior results.

Other materials may be incorporated in the compositions of thisinvention depending upon the properties desired in the finished articlesfabricated from the compositions. Thus, it has been found that finelydivided solid fillers, pigments, dyes, other lubricants (e. g., siliconeoils (polyorga'nosiloxanes), high-boiling esters such as dibutylphthalate and tricresyl phosphate. naturally occurring low-meltingwaxes, and fluorinated hydrocarbon oils, all of which should have aviscosity of 0.45 to 1000 centipoises at 25 0.), plasticizers, and thelike may be added to the compositions in varying amounts. Examples ofsuitable fillers and pigments which may thus be employed include carbonblack, graphite, mica, talc, silica, asbestos, and titanium dioxide. Allof these fillers and pigments should be in finely divided form andpreferably should be of the approximate particle size of the polymerused in the mixture. The fillers and pigments be employed in amountsvarying from relatively small amounts up to as much as 400%, based onthe dry Weight of the tetrafiuoroethylene polymer in the composition.All of these additional modifiers may be incorporated into thecomposition at any time prior to fabrication into the finished article.The fillers and pigments serve either to color the polymer or to extendand reinforce the polymer, resulting in mixtures having increasedelongation in some cases and in mixtures having a lower cost where acheap filler is selected. However, if the best electrical propertiesinherent in the polytetrafluoroethylene are desired, it will generallynot be practical to employ large amounts of these other additives.

The chief advantage of this invention is that thepolytetrafiuoroethylene compositions may readily be extruded atrelatively low temperatures (1. e., at 15 C. to 150 C.) under compactingpressure into various shapes at rates up to and sometimes over 50 feetper minute, whereas prior to this invention melt extrusion rates werelimited to approximately 50 feet per hour at much higher temperatures.These extruded shapes may readily be freed from all hydrocarbons byeither volatilizing the hydrocarbon or extracting the hydrocarbon with asolvent. Following removal of the hydrocarbon the shaped article isbaked at a temperature above 327 C. until sintered, and

thereafter either annealed or quenched. The process of preparingextruded articles from lubricated polytetrafiuoroethylene is more fullydescribed and claimed in U. S. Serial No. 171,534, filed by Llewellynand Lontz on June 30, 1950.

Another advantage of this invention is that the compositions provide ameans for molding polytetrafluoroethylene at temperatures as low as roomtemperature and above into useful articles, following which thehydrocarbon may be removed as above and the article finally sintered ata temperature above 327 C. Still another advantage of the compositionsof this invention lies in the fact that they may be calendered overasbestos, paper, cloth, foil and the like, following which thehydrocarbon may be removed as above and the extruded article sintered ata temperature above 327 C. if desired. For example, the composition maybe coated by spreading, by using a doctor knife, or by rollin thecomposition onto supporting structures such as asbestos cloth, webbing,boards, porous ceramic surfaces, glass cloth, metal screens, and thelike.

The compositions of this invention are useful for extrusion into variousforms such as filaments, l

beading, films, sheets, tubes, rods, tapes; extrusion coatings on wires,calender rolling into sheets; coating and calendering over paper, cloth,foil, and the like; and for molding into various articles. tion involvesuse of the compositions for bonding or repairing sections ofpolytetrafiuoroethylene film or sheeting. For example, several sectionsof an unbaked, unsintered sheet extruded from one of the lubricatedpolymer compositions of this in- Another particularly suitableapplicavention have been lapped and securely bonded to give satisfactorybonds.

Another application for the compositions of this invention involves asimplified method for joining spliced sections ofpolytetrafluoroethylene coated Wire conductors. This method involves thesteps of wrapping the spot to be spliced with one or more layers ofunsintered lubricated polytetrafiuoroethylene tape extruded from one ofthe lubricated compositions of this invention, and thereafter heatingthe resulting assembly above 327 C. to sinter the whole and effectbonding to the conductor and its coating. The same Wrapping techniquemay be applied to the covering of other metal articles such an ironmagnets, coils, and the like Where it is desired to cover the articlewith a chemically-inert, corrosion-resistant, electrical insulatingcovering.

We claim:

1. A process for preparing a non-aqueous pressure-coalescing compositionwhich comprises contacting dry tetrafiuoroethylene polymer particles ofcolloidal size with an atmosphere comprising a mist of at least oneessentially saturated hydrocarbon having a boiling point of 220 C. to400 C. at atmospheric pressure from the group consisting of aliphaticand cycloaliphatic hydrocarbons, and intimately mixing said polymerparticles and hydrocarbon mist until a uniform intimate mixture isobtained in the form of a dry, free-flowing powder, the weight of saidhydrocarbon being from 15% to 30% of the combined weight of saidtetrafluoroethylene polymer and hydrocarbon.

2. The process of claim 1 in which the mixing of said polymer particleswith said hydrocarbon is accomplished by spraying a mist of thehydrocarbon onto the polymer particles while the particles are beingtumbled.

3. The process of claim 1 in which the said hydrocarbon has a boilingpoint of 250 C. to 300 C. at atmospheric pressure.

4. The process of claim 1 in which the said hydrocarbon is a mixture ofhydrocarbons having a boiling range of 252 C. to 274 C. at atmosphericpressure.

5. The process of claim 1 in which the said tetrafluoroethylene polymeris polytetrafluoroethylene.

JOHN FRANK LONTZ. LESTER EUGENE ROBB.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,230,654. Plunkett Feb. 4, 19412,510,078 Compton et al June 6, 1950

1. A PROCESS FOR PREPARING A NON-AQUEOUS PRESSURE-COALESCING COMPOSITIONWHICH COMPRISES CONTACTING DRY TETRAFLUOROETHYLENE POLYMER PARTICLES OFCOLLOIDAL SIZE WITH AN ATMOSPHERE COMPRISING A MIST OF AT LEAST ONEESSENTIALLY SATURATED HYDROCARBON HAWVING A BOILING POINT OF 220* C. TO400* C. AT ATMOSPHERIC PRESSURE FROM THE GROUP CONSISTING OF ALIPHATICAND CYCLOALIPHATIC HYDROCARBONS, AND INTIMATELY MIXING SAID POLYMERPARTICLES AND HYDROCARBON, MIST UNTIL A UNIFORM INTIMATE MIXTURE ISOBTAINED IN THE FORM OF A DRY, FREE-FLOWING POWDER, THE WEIGHT OF SAIDHYDROCARBON BEING FROM 15% TO 30% OF THE COMBINED WEIGHT OF SAIDTETRAFLUOROETHYLENE POLYMER AND HYDROCARBON.